The present invention relates to the migration of a logical volume that is connected to a host computer.
In recent years, the amount of data saved in computer systems has been increasing rapidly. Hence, storage systems with large-scale storage capacities have been adopted in computer systems that store increasing amounts of data.
Storage systems provide storage areas in units called logical volumes in host computers. Generally, the storage capacity of logical volumes is fixed but the technology disclosed in Japanese Patent Application Laid Open No. 2003-015915 for increasing the usage efficiency of storage areas, that is, technology for automatically expanding the storage capacity of logical volumes by allocating a partial area (‘segment’ hereinbelow) of a physical resource to a logical volume in accordance with an access request from a host computer has been invented. Further, in this specification, a logical volume of expanded capacity is known as a ‘capacity-expansion volume’. A capacity-expansion volume is a logical volume that can be provided by Thin Provisioning Technology and a capacity-expansion volume is also called a ‘Thin Provisioning volume’. Further, the ‘physical resources’ as they are called in this specification are logical storage devices (logical devices) that are provided on a physical storage area. A physical storage area may be a storage area that is provided by one physical storage device or may be a storage device that is provided by a RAID group that is a group that complies with RAID (Redundant Array of Independent Disks) rules (also called a ‘parity group’ or an ‘array group’). A RAID group is a storage device group that is constituted by a plurality of physical storage devices (hard disk drives, for example).
However, when an operation that uses a storage system is continued, data of a low usage frequency is sometimes saved as is on a highly reliable, responsive and durable expensive disk. In this case, there is the problem that the expensive disk capacity is used more than is necessary and the expensive disk cannot be used efficiently. Hence, a technology that migrates data from the expensive disk to an inexpensive disk the reliability, responsiveness, and durability of which are inferior to those of the expensive disk has been invented (See Japanese Patent Application Laid Open No. 2003-345522, for example).
Further, when a fault occurs in a first storage system or the like, for example, the capacity-expansion volume connected to the host computer is migrated from the first storage system to a second storage system. More specifically, the capacity-expansion volume connected to the host computer is switched from the first capacity-expansion volume in the first storage system to the second capacity-expansion volume in the second storage system, for example.
When the capacity-expansion volume is migrated, the host computer must also read data that is the same as the data read from the capacity-expansion volume of the first storage system from the capacity-expansion volume of the second storage system. Methods for implementing this reading include a method that migrates data in the migration-source capacity-expansion volume to the migration-destination capacity-expansion volume.
However, the following two problems exist with this method.
The first problem is that a data copy is produced between storage systems That is, the migration of data ends as a result of copy-source data being deleted when data is copied between storage systems. Therefore, the data copying takes time and there is a load on the storage system. This is a larger problem when the data to be migrated exists in large quantities.
As a second problem, when an external connection function (described subsequently) is installed in the first and second storage systems and first and second external storage systems are connected to the first and second storage systems, an area that is blank enough to provide the second external volume, which has the same storage capacity as the external storage device comprising data to be migrated (the logical volume in the first external storage system, for example) must be provided in the second external storage system. Hence, when such a blank area cannot be provided in the second external storage system, data cannot be migrated and, consequently, the capacity-expansion volume connected to the host computer cannot be switched.